The present invention relates generally to the repair of a dovetail slot in a gas turbine engine disk and, more particularly, to an apparatus and method of removing a predetermined amount of material from a bottom portion of such dovetail slot.
It has been found that heavily cold worked material and other characteristics having the capability to reduce low cycle fatigue in dovetail slots of gas turbine engine disks, and particularly turbine disks which are rotated, may be caused during generation of such dovetail slots. In particular, the disturbed material may be caused by a dull broach tool during formation of the dovetail slot. Conventional methods of removing such disturbed material include milling the dovetail slot or to broach it again. Each of these processes, however, are useful only so long as the tools employed are sharp. Further, a hand deburr operation is typically required, which inherently involves a high risk of creating tool marks in the highly stressed dovetail area.
It is known in the art to utilize a flow of abrasive material on surfaces of gas turbine engine components in order to polish or provide surface finishing thereof. Such operations involve removing only a minimal amount of material (e.g., on the order of 0.0005 inch or 0.5 mil). An example of one such method is disclosed in U.S. Pat. No. 6,183,347 to Shaw, where a stream of pliant shot in a carrier fluid is discharged at a shallow angle of incidence against a plug and an adjoining surface for selective abrasion to provide a step. It will be appreciated therein that the method described is for the selective surface treating of a workpiece and does not involve the removal of material on the order required to remove a disturbed layer of material or shallow cracks.
While the aforementioned methods of removing disturbed material from a gas turbine engine disk are useful for that particular purpose, it would be desirable for an improved method of removing such disturbed material to be developed which overcomes the limitations noted above. It would also be desirable for an apparatus to be developed which defines a flow path through the dovetail slot in a manner which permit substantially uniform removal of the material in a surface on a bottom portion thereof without affecting the pressure surface portion of the dovetail slot.
In a first exemplary embodiment of the invention, a method of removing a predetermined amount of material from a bottom portion of a dovetail slot in a gas turbine engine disk is disclosed as including the steps of configuring a designated flow path through the dovetail slot and providing a flow of abrasive media through the flow path for a designated number of cycles so that a substantially uniform amount of material is removed from the dovetail slot bottom portion. The method also includes the step of sealing a pressure surface of the dovetail slot to prevent the abrasive media from flowing thereagainst.
In a second exemplary embodiment of the invention, an apparatus for removing a predetermined amount of material from a bottom surface of a dovetail slot in a gas turbine engine disk is disclosed, wherein a longitudinal axis extends through the dovetail slot. The system includes a fixture for providing a flow of abrasive media back and forth through a designated path at a predetermined pressure and flow rate, a cradle for retaining the gas turbine engine disk in position so that the dovetail slot is in flow communication with the designated path, and a device for defining a designated flow path through the dovetail slot for the abrasive media. The flow of abrasive media then removes a substantially uniform amount of material from a bottom surface of the dovetail slot. The designated path of the abrasive flow fixture is configured to enable work on each dovetail slot of the disk to be performed substantially simultaneously.